As is well known, flat panel displays (FPDs) have become mainstream as image display devices in recent years, the FPDs being typified by a liquid crystal display, a plasma display, an organic light-emitting diode (OLED) display, and the like. As substrates for those FPDs, glass substrates are used in order to secure various demanded properties such as airtightness, flatness, heat resistance, translucency, and insulation property. Further, in view of reducing a weight, the glass substrates to be used for the FPDs are currently becoming thinner. In particular, the FPDs such as an OLED display may be used under a state in which a display screen is bent, and hence thinning of the glass substrates has been expected for the purpose of imparting flexibility to the glass substrates.
Further, there is a growing use of an OLED as a plane light source, such as a light source for interior illumination, which emits only monochrome (for example, white) light, unlike a display that uses TFTs to blink light of three fine primary colors. Further, when an OLED illumination device includes a glass substrate having flexibility, a light-emitting surface is freely deformable, which leads to an advantage in that the OLED illumination device is usable for a significantly wider range of applications. Therefore, from the viewpoint of ensuring sufficient flexibility, there is also promoted further thinning of the glass substrate to be used for the illumination device of this type.
In addition, operation of a touchscreen is performed by rubbing a surface of the touchscreen with human fingers and the like, and hence a glass substrate is often used in order to ensure fastness property of the surface of the touchscreen. Along with widespread use of mobile devices equipped with a touchscreen of this type, thinning of the glass substrate for the touchscreen is required for reduction in weight of the mobile devices.
In response to the above-mentioned demands for thinning, a glass film thinned into a film shape (for example, having a thickness of 300 μm or less) has been developed. The glass film has appropriate flexibility, and hence is sometimes stored in a state of a so-called glass roll that is formed by superposing a protective film on the glass film, and rolling the glass film together with the protective film around a roll core (for example, see Patent Literature 1). This reduces a storage space for the glass film remarkably, and hence it is possible to increase transportation efficiency. Further, with use of a roll-to-roll apparatus, various processes such as cutting and film formation can be sequentially performed on a glass film that is unrolled from a glass roll situated on an upstream side, and hence it is possible to remarkably increase production efficiency.